Taxonomy & naming
Hemipsilichthys papillatus was described by Pereira, Oliveira and Oyakawa in 2000, in Ichthyological Exploration of Freshwaters (volume 11, number 4, pages 377–383). The Catalog of Fishes (Eschmeyer, CAS) carries a valid species link for the name (spid 65999).
The genus Hemipsilichthys is placed by FishBase in the subfamily Delturinae of the Loricariidae, a small subfamily of southeastern Brazilian armoured catfishes. The specific epithet papillatus refers to the distinctively shaped papillae on the lower lip.
Morphology
Hemipsilichthys papillatus reaches a maximum length of about 3.5 in standard length. Published meristics give a dorsal fin with 7 soft rays and an anal fin with 5 soft rays. The dorsal series of plates is reduced — there are no plates between the dorsal-fin origin and the end of the adipose fin — and the teeth cusps are approximately equal. The lower lip bears distinct, characteristically shaped papillae, the feature for which the species is named.
No data on sexual dimorphism is published in the sources consulted.
Habitat
The species occurs in eastern Brazilian coastal drainage, in the Paraíba do Sul basin, with the type locality in Minas Gerais, Brazil. It inhabits small, shallow streams with clear water and moderate-to-strong current, over a bottom of rocks, loose stones and gravel, with forest and grass margins.
Feeding
No detailed feeding study is published for Hemipsilichthys papillatus, and dietary data is sparse. Its loricariid body plan and rocky, fast-flowing stream habitat are consistent with a benthic grazer feeding on algae and biofilm rasped from the substrate, but specific observations are lacking in the sources consulted.
Mating
No data on courtship or mating behaviour has been published for this species.
Breeding
No breeding data has been published for Hemipsilichthys papillatus in the sources consulted.
In the aquarium
Hemipsilichthys papillatus is not an aquarium species and has no record of hobby maintenance in the sources consulted. As a range-restricted, Near Threatened fish of coastal Atlantic drainages, it is not an appropriate subject for the aquarium trade, and any inference about captive care would be speculative.
Conservation
The IUCN Red List assessed Hemipsilichthys papillatus as Near Threatened (NT) under criterion B1b(iii), with the assessment dated 7 November 2018.
The listing reflects the species' restricted distribution within the Paraíba do Sul coastal drainage of southeastern Brazil. Streams in this region are subject to habitat alteration and water-quality decline, the principal pressures on narrowly distributed loricariids of this kind.